Changelog for tzdata: 2026c -> 2026d
Source: NEWS

Release 2026d - 2026-09-11 15:21:07 -0700

  Briefly:
    Canada’s Northwest Territories moved to permanent -06 on 2026-08-21.
    Obsolescent settings like TZ="EST5EDT" now conform better to POSIX.
    Fix security, performance and porting bugs in zic and localtime.

  Changes to future timestamps

    Canada’s Northwest Territories will not fall back on 2026-11-01
    and will stay on -06 year-round, matching Alberta’s recent change.
    Model this with its traditional abbreviation CST.  Although the
    change to permanent -06 legally took place on 2026-08-21,
    temporarily model the change to occur on 2026-11-01 at 02:00
    for the same reason as other recent temporary hacks.  (Caution:
    see “NOTE FOR 2026b TEMPORARY HACK FOR CLDR AND CANADA” below.)
    This affects only America/Inuvik as the rest of the territory is
    covered by America/Edmonton, for which the equivalent change was
    released in 2026c.

  Changes to past timestamps

    Colombia’s 1992-05-02 spring forward was at 00:00, not 24:00.

    Iran’s 1979-05-26 spring forward was at 00:00, not 24:00.
    (Thanks to N.F. Hase.)

    The backward-compatibility names EST5EDT, CST6CDT, MST7MDT, and
    PST8PDT now conform better to POSIX.  For example, EST5EDT now
    always uses the abbreviation "EST" for standard time (now always 5
    hours behind UT) and "EDT" for daylight saving time, whereas it
    formerly had different UT offsets before standard time was
    introduced and sometimes used abbreviations like "LMT", "EWT" and
    "EPT", all contrary to POSIX.  Also, though not required by POSIX
    these names now use US federal rules rather than rules of places
    like New York, reverting to 2024a behavior.  This change affects
    only timestamps before 1966-10-30 at 01:00 standard time.

  Other data changes

    The temporary hacks used for North American timekeeping changes
    now work around a libstdc++ std::chrono bug in GCC 14.1-14.4,
    15.1-15.2, and 16.1; see GCC bug 124851.  This data change does
    not affect TZif files or timestamps.  The change does not work
    around the related but less serious GCC bugs 116110 and 124513.
    These GCC bugs are all fixed in GCC 16.2.

  Changes to code

    zic now rejects Link targets that would have invalid names, and
    more efficiently processes Expires, Leap and Rule lines with years
    far in the past or future.  (Thanks to Darren Carreras.)

    zic now ports to systems that report lack of link support via
    EINVAL, ENOSYS or EPERM errno values. (Thanks to Tom Lane.)

    When tzset and related functions encounter a TZif file that is too
    large for them, they now consistently fail instead of sometimes
    silently ignoring excess parts of the file.

    localtime-related functions no longer mishandle extreme timestamps
    when given TZif files holding some unlikely timezone histories.
    (Problem reported by David Sarkisyan.)

    localtime-related functions no longer check the values of TZif
    files’ standard/wall and UT/local indicators, which these
    functions have not used since 2026a’s removal of the old
    posixrules feature.

    tzcode has been ported to Haiku.

    localtime.c now works again by default on AIX and DragonFly BSD.

    zic now rejects ‘:’ and ‘\’ in Zone and Link names when running on
    Microsoft Windows.  (Problem reported by David Diaz.)

  Changes to documentation

    URLs for release tarballs in tz-link.html have been updated to
    reflect their new canonical URLs on data.iana.org.

    temporary hack for British Columbia in 2026b.  (Caution: see
    “NOTE FOR 2026b TEMPORARY HACK FOR CLDR AND CANADA” below.)

      As the change affects both America/Edmonton and its backward
      compatibility link, the obsolescent setting TZ="Canada/Mountain"
      will now use the abbreviation CST for affected timestamps,
      akin to TZ="Canada/Pacific" behavior introduced in 2026b.
    zic no longer mishandles a last transition to a new time type.
      To match longstanding practice for -07 standard time in North
      America, such as for America/Dawson, America/Dawson_Creek,
      America/Fort_Nelson and America/Whitehorse, affected BC
      timestamps use the abbreviation MST.  As the change affects both
      America/Vancouver and its backward compatibility link, the
      obsolescent setting TZ="Canada/Pacific" will now use the
      abbreviation MST.  Future TZDB releases may change the
      abbreviation if something else becomes popular across areas
      observing -07, and may change it to "-07" if no alphabetic
      consensus emerges.

    NOTE FOR 2026b TEMPORARY HACK FOR CLDR AND CANADA:
    This zic fix is needed for the temporary hack (mentioned above)
    that works around the Canadian timekeeping bug in Unicode CLDR.
    Without the fix, the temporary hack causes zic versions 2023d
    through 2026a, in their default mode that generates slim output,
    to generate a TZif file that violates Internet RFC 9636 §3.3.
    The buggy file in turn causes some TZif readers, including tzcode
    itself, to ignore America/Vancouver’s 2026-11-01 02:00 transition
    from PDT (tm_isdst=1) to MST (tm_isdst=0).  Although the buggy
    file does not cause any known TZif reader to mishandle UT offsets,
    caution is advised when using zic 2023d through 2026a to compile
    data from more-recent tz releases.  To work around this problem
    when using these older zic versions, use ‘zic -b fat’.